The party's ideology combines environmentalism with left-wing economic policies, including well-funded and locally controlled public services.

In 2010, the party gained its first member of Parliament in its then-leader Caroline Lucas (although Plaid Cymru's Cynog Dafis was elected on a joint ticket in the 1990s).

[27] In Wales, the Greens endorsed Plaid Cymru candidate Cynog Dafis in the 1992 general election, having worked with him on several environmental initiatives.

[32] Although this dropped to two following the 2004 London Assembly elections, the Green AMs proved vital in passing the annual budget of former Mayor Ken Livingstone.

[40] In the 2011 local government elections in England and Wales, the Green Party in Brighton and Hove took minority control of the City Council by winning 23 seats, five short of an overall majority.

[75] Lucas first suggested "progressive pacts" to work on a number of issues including combating climate change and for electoral reform, following the results of the 2015 general election.

[74] Following the vote to leave the European Union in June 2016, Bennett published an open letter, calling for an "anti-Brexit alliance" potentially comprising Labour, the Liberal Democrats and Plaid Cymru to stand in a future snap election in English and Welsh seats.

[101] In the south west the Greens became the largest party on Bristol City Council failing to win an outright majority by a single seat.

[108] Along with Brighton Pavilion, the Greens targeted three other seats in the general election: Bristol Central, Waveney Valley and North Herefordshire.

[109] In what turned out to be the Greens' best ever general election, Berry held Brighton Pavilion, while Denyer gained Bristol Central, defeating Labour incumbent and Shadow Culture Secretary Thangam Debbonaire;[110] Ramsay won Waveney Valley, a notional gain from the Conservatives,[111] and Ellie Chowns won North Herefordshire, defeating Conservative incumbent Bill Wiggin.

[112] Sociologist Chris Rootes stated that the Green Party took "the left-libertarian" vote,[113] while Dennison and Goodwin characterised it as reflecting "libertarian-universalistic values".

[114] The party wants an end to big government, which it sees as hindering open and transparent democracy, instead devolving and decentralising power to a more local level.

They also want to limit the power of big business, which, they argue, upholds the unsustainable trend of globalisation, and is detrimental to local trade and economies.

[120] For the 2019 general election, the party's manifesto had four key sections: "remain and transform", which advocated for the UK to reverse its decision to leave the EU and increase cross-border co-operation with the EU; "grow democracy", which aimed to overhaul the UK's current voting system and rebalance government power by lowering the voting age from 18 to 16 and redefining the jurisdiction of local governments; the "green quality of life guarantee", which addressed social issues such as housing, the NHS, education, countryside conservation, discrimination, crime, drug reform, animal rights, and the implementation of a universal basic income; and the "new deal for tax and spend", which outlined the party's economic policies such as simplifying income tax, increasing corporation tax to make big businesses pay their fair share, supporting small businesses, and ending wasteful spending.

Their manifesto focused on providing a "secure future", solving the climate crisis, major investment into the NHS, raising tax in those earning over £50,270 a year, nationalising Britain's railways, water companies and largest energy companies, expanding renewable power, campaigning for councils to be given the right to set rent controls and ban no-fault evictions.

[129] In November 2019, the Greens pledged to introduce a universal basic income by 2025, which will give every adult in the United Kingdom (unemployed or not) at least £89 a week (with additional payments to those facing barriers to work, including disabled people and single parents).

[130] The policy also aims to tackle the rising levels of automation that threaten to put millions out of work and fundamentally change British industry.

[136] The party also wants to set new air quality standards, increase the number of forests and woodlands in England and Wales and extend people's access to green space.

[115] The Green Party advocate for a less "bully boy culture" from the Western world and more self-sustainability in terms of food and energy policy on a global level, with aid, only being given to countries as a last resort in order to prevent them from being indebted to their donors.

[153] This sits alongside the party's belief that adults should be free to make informed decisions about their own drug consumption, while this freedom is also balanced with the government's responsibility to protect individuals and society from harm.

[158] The 2015 and 2017 general election manifestos contained policies on all teachers to be trained on LGBTIQA+ issues (such as "providing mandatory HIV, sex, and relationships education – age appropriate and LGBTIQA+-inclusive – in all schools from primary level onwards"), on reforming the system of pensions, on ending the "spousal veto" (a provision of the Gender Recognition Act that requires applications for a Gender Recognition Certificate to include written consent from an applicant's spouse)[159] and on "mak[ing] equal marriage truly equal" by amending pension inheritance rights.

[165][166][167] In the subsequent leadership election, candidate Shahrar Ali's comments on trans rights led to the Young Greens to call for his expulsion.

[177] The party was, however, in favour of high speed rail in principle, as a means of challenging short haul domestic flights, provided projects meet strict criteria.

[184]The party campaigns for greater accountability in global governance, with the United Nations made up of elected representatives and more regional representation, as opposed to the current nation-based setup.

[115] The party advocates ending the first past the post voting system for UK parliamentary elections and replacing it with a form of proportional representation.

[192] The party's general policy is to support the self-determination of Scotland, Wales and Northern Ireland, should they wish to secede from the United Kingdom.

[195] The party supported the 2016 referendum on the United Kingdom's membership of the European Union, calling it "a vital opportunity to create a more democratic and accountable Europe, with a clearer purpose for the future".

[citation needed] In 2013, then party leader, Natalie Bennett added that: 'Yes to the EU' does not mean we are content with the union continuing to operate as it has in the past.

[232] In 1995, sociologist Chris Rootes stated that the Green Party "appeals disproportionately to younger, highly educated professional people"; however, he noted that this support base was "not predominantly urban".

In May 2014, Taylor and Lambert held their seats, and were joined by Molly Scott Cato who was elected in the South West region, increasing the number of Green Party Members of the European Parliament to three for the first time.